ata.c

#include "bootloader.h"

/* TODO: Add support for drives other than the master on the primary bus. */
static const int ata_io_base = 0x1F0;
static const int ata_control_base = 0x3F6;

static uint16_t ata_identify_data[256];

static void ata_delay()
{
    for (int i = 0; i < 15; i++)
        inb(ata_io_base + 7);
}

static void ata_poll()
{
    /* Wait for either ERR, DF, or DRQ */
    uint8_t status;
    while (true) {
        status = inb(ata_io_base + 7);
        if (!(status & 0x80) && (status & 0x29)) break;
    }

    if (status & 0x21) {
        boot_error("Boot device I/O error");
    }
}

void ata_init()
{
    /* Check for floating bus. */
    if (inb(ata_io_base + 7) == 0xFF) goto fail;

    /* Select the master drive. */
    outb(ata_io_base + 6, 0xA0);
    ata_delay();

    outb(ata_io_base + 2, 0);
    outb(ata_io_base + 3, 0);
    outb(ata_io_base + 4, 0);
    outb(ata_io_base + 5, 0);

    /* Issue IDENTIFY DEVICE command. */
    outb(ata_io_base + 7, 0xEC);

    if (inb(ata_io_base + 7) == 0) goto fail;

    /* Wait for BSY to clear. */
    while (inb(ata_io_base + 7) & 0x80) {}

    if (inb(ata_io_base + 4) || inb(ata_io_base + 5)) goto fail;

    ata_poll();

    for (int i = 0; i < 256; i++) {
        ata_identify_data[i] = inw(ata_io_base);
    }
    screen_println("Found hard drive");

    outb(ata_control_base, 0);
    return;
fail:
    boot_error("Boot device not found");
    return;
}

void ata_read_sector(uint32_t lba, void *buffer)
{
    /* Select drive, LBA bit on */
    outb(ata_io_base + 6, 0xE0 | ((lba >> 24) & 0x0F));
    ata_delay();

    outb(ata_io_base + 2, 1); /* sector count */
    outb(ata_io_base + 3, lba & 0xFF); /* LBAlo */
    outb(ata_io_base + 4, (lba >> 8) & 0xFF); /* LBAmid */
    outb(ata_io_base + 5, (lba >> 16) & 0xFF); /* LBAhi */

    outb(ata_io_base + 7, 0x20); /* READ SECTORS command */
    ata_poll();
    for (int i = 0; i < 256; i++) {
        uint16_t word = inw(ata_io_base);
        ((unsigned char *)buffer)[i * 2] = word & 0xFF;
        ((unsigned char *)buffer)[i * 2 + 1] = (word >> 8) & 0xFF;
    }
    ata_delay();
}